Immersion liquid, exposure apparatus, and exposure process

ABSTRACT

An immersion liquid is provided comprising an ion-forming component, e.g. an acid or a base, which has a relatively high vapor pressure. Also provided are lithography processes and lithography systems using the immersion liquid.

This application is a continuation of U.S. patent application Ser. No.15/250,579, filed Aug. 29, 2016, now allowed, which is a continuation ofU.S. patent application Ser. No. 14/885,775, filed Oct. 16, 2015, nowU.S. Pat. No. 9,454,088, which is a continuation of U.S. patentapplication Ser. No. 14/504,130, filed Oct. 1, 2014, now U.S. Pat. No.9,164,391, which is a continuation of U.S. patent application Ser. No.11/883,944, filed on Jun. 17, 2008, now U.S. Pat. No. 8,859,188, whichis the U.S. National Phase of PCT Patent Application No.PCT/EP2006/001005, filed Feb. 6, 2006, which is a continuation of U.S.patent application Ser. No. 11/071,044, filed on 3 Mar. 2005, whichclaims the benefit of priority of U.S. Provisional Patent Application60/651,513, filed on Feb. 10, 2005, each of the foregoing applicationsis hereby incorporated in its entirety by reference.

FIELD

The invention relates to immersion liquids, exposure apparatus, andexposure processes.

BACKGROUND

Immersion lithography is gaining attention due to improvements incritical dimensions and/or depth of focus that it provides. However, thetechnology also faces some concerns. For instance, on the one hand anultra-pure immersion liquid may be advantageous to minimize theappearance of stains when drying areas wetted by the liquid, but on theother hand it may be desirable to include additives in the immersionliquid to influence or create desirable properties. E.g., it may bedesirable to include acid components in the immersion liquid to avoid orminimize so-called T-topping or other undesirable effects. T-topping,for instance, may occur when a resist layer on a substrate to be exposedto radiation comes into contact with the immersion liquid and componentsin the resist (e.g. photo-acid generators) diffuse or dissolve into theimmersion liquid. See also EP 1 482 372 A1.

Accordingly, objectives of the invention include providing an immersionliquid comprising one or more additives yet having reduced stainingconcerns.

Also, objectives of the invention include avoiding or minimizingstreaming potential effects caused by the flow of immersion liquid(discussed in more detail infra).

SUMMARY

The invention provides immersion liquids, exposure apparatus, andexposure processes.

In an embodiment, the invention provides an immersion liquid formed by amethod comprising adding an ion-forming component to a liquid (e.g. anaqueous liquid), wherein the ion-forming component has a vapor pressuregreater than 0.1 kPa, e.g. greater than water.

In an embodiment, the invention provides an immersion liquid having a pHbelow 7, the pH below 7 being at least partly caused by a componenthaving a vapor pressure greater than 0.1 kPa, e.g. greater than water.

In an embodiment, the invention provides an immersion liquid having a pHgreater than 7, the pH greater than 7 being at least partly caused by acomponent having a vapor pressure greater than 0.1 kPa, e.g. greaterthan water.

In an embodiment, the invention provides an immersion liquid having anelectric conductivity of at least 0.1 μS/cm, e.g. at least 1.3 μS/cm at25° C. In an embodiment, the invention provides an immersion liquidhaving an electric conductivity in the range of 0.1-100 μS/cm at 25° C.,e.g. in the range of 1.3-100 μS/cm at 25° C. In an embodiment, theconductivity is at least partly caused by a component having a vaporpressure greater than 0.1 kPa, e.g. greater than water.

Also, the invention provides processes, e.g. an immersion lithographyprocess, using the immersion liquids. In an embodiment, the inventionprovides a device manufacturing process comprising exposing aphotosensitive substrate to radiation, wherein the radiation has passedthrough the immersion liquid prior to reaching the substrate.

In addition, the invention provides immersion lithography systemscomprising an immersion lithography apparatus and one or more of theimmersion liquids.

In an embodiment, the invention provides a process comprising:

-   -   (i) adding a component to a liquid, the component having a vapor        pressure greater than 0.1 kPa, e.g. greater than water;    -   (ii) exposing a photosensitive substrate to radiation, wherein        the radiation has passed through the aqueous liquid comprising        the component prior to reaching the photosensitive substrate;

wherein the adding of the component increases the ion concentration inthe liquid.

In an embodiment, the invention provides a process comprising:

-   -   (i) adding an acid to a liquid, the acid having a vapor pressure        of at least 0.1 kPa, e.g. at least 5 kPa;    -   (ii) exposing a photosensitive substrate to radiation, wherein        the radiation has passed through the liquid comprising the        component prior to reaching the photosensitive substrate.

In an embodiment, the invention provides a process comprising:

-   -   (i) patterning a beam of radiation;    -   (ii) passing the patterned beam of radiation through a liquid        (e.g. an aqueous liquid), the liquid comprising ions formed by a        component having a vapor pressure greater than 0.1 kPa, the        conductivity of the liquid being at least 0.25 μS/cm;    -   (iii) exposing a photosensitive substrate to the patterned beam        of radiation.

In an embodiment, the invention provides an immersion lithography systemcomprising:

-   -   (i) an immersion lithography exposure apparatus; and    -   (ii) an immersion liquid, e.g. an immersion having an electric        conductivity in the range of 0.1-100 μS/cm at 25° C. (for        instance in the range of 1.3-100 μS/cm at 25° C.) or a carbon        dioxide enriched immersion liquid.

In an embodiment, the invention provides a lithography apparatus havinga voltage generator capable of applying a voltage difference between afirst part of a lithography apparatus, e.g. a substrate table, and asecond part of the lithography apparatus, e.g. an immersion hood of animmersion lithography apparatus. In an embodiment, the inventionprovides a process comprising applying a voltage difference between afirst part of a lithography apparatus, e.g. the substrate table, and asecond part of the lithography apparatus, e.g. the immersion hood of animmersion lithography apparatus.

Additional objects, advantages and features of the invention are setforth in this specification, and in part will become apparent to thoseskilled in the art on examination of the following, or may be learned bypractice of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 represents an immersion lithography system according to anembodiment of the invention.

FIG. 2 represents an embodiment of an immersion hood of an immersionlithography system according to an embodiment of the invention.

DETAILED DESCRIPTION

Preliminarily, this application at various instances refers to vaporpressures of components. In this regard, the vapor pressure of acomponent refers to the vapor pressure of a component in its pure form(thus not in a mixture or in solution) at 20° C.

In an embodiment, the invention provides an immersion liquid. Also, theinvention provides a process using an immersion liquid, e.g. animmersion lithography process.

IMMERSION LIQUID

In an embodiment, the immersion liquid is prepared by a processcomprising adding one or more components to a liquid, e.g. an aqueousliquid, for instance a liquid comprising, relative to the total weightof the liquid, at least 50 wt % water, such as at least 75 wt % water,at least 90 wt % water, at least 95 wt % water, at least 99 wt % water,at least 99.5 wt % water, at least 99.9 wt % water, or at least 99.99 wt% water. In an embodiment, the liquid, before adding the one or morecomponents, has an electric conductivity of less than 0.1 μS/cm (asdetermined at 25° C.). In an embodiment, the liquid is de-gassed beforeadding the one or more components. In an embodiment, the liquid ispurified before adding the one or more components. In an embodiment, theliquid is ultra-pure, de-gassed water.

In an embodiment, the component added to the liquid has a relativelyhigh vapor pressure. A high vapor pressure may assist, e.g., in avoidingstains on a substrate when immersion liquid is removed (e.g.,evaporated) from the substrate. In an embodiment, the component added tothe liquid has a vapor pressure exceeding the vapor pressure of theliquid it is added to. In an embodiment, the component added to theliquid has a vapor pressure of at least 0.1 kPa, e.g. at least 0.25 kPa,at least 0.5 kPa, at least 0.75 kPa, at least 1 kPa, at least 1.3 kPa,at least 1.5 kPa, at least 1.8 kPa, at least 2.1 kPa, or exceeding thevapor pressure of water (i.e., exceeding 2.34 kPa). In an embodiment,the component added to the liquid has a vapor pressure of at least 3.5kPa, such as at least 5 kPa, at least 10 kPa, at least 20 kPa, at least30 kPa, or at least 50 kPa. In an embodiment, the component being addedis formic acid or acetic acid. In an embodiment, the component added tothe liquid is, in its pure form at 20° C. and at 1 atmosphere pressure,a gas. In an embodiment, the component added to the liquid is carbondioxide. In an embodiment, the immersion liquid comprises, relative tothe total weight of the immersion liquid, less than 5 wt % of componentshaving a vapor pressure below 2.0 kPa (e.g. below 1.5 kPa, below 1 kPa,below 0.5 kPa, below 0.25 kPa, below 0.1 kPa, or 0 kPa), e.g. less than3 wt %, less than 1 wt %, less than 0.5 wt %, less than 0.25 wt %, lessthan 0.1 wt %, less than 0.05 wt %, less than 0.025 wt %, less than 0.01wt %, or less than 0.005 wt %. In an embodiment, the immersion liquidcomprising the component having a relatively high vapor pressure is, nottaking into account the main constituent of the immersion liquid (e.g.,water in an immersion liquid having water as the main constituent),essentially absent components having a vapor pressure below 2.0 kPa,e.g. below 1.5 kPa, below 1 kPa, below 0.5 kPa, below 0.25 kPa, below0.1 kPa, or 0 kPa.

In an embodiment, the component added to the liquid promotesconductivity of the liquid, e.g. by promoting ion formation. Increasedconductivity of the immersion liquid may assist in decreasing oravoiding streaming potential concerns. Streaming potential is discussedin, e.g., the article “Streaming Potential Cells For The Study ofErosion-Corrosion Caused By Liquid Flow” by Varga and Dunne in J. Phys.D: Appl. Phys., 18 (1985), p. 211-220. Streaming potential may, e.g.,shorten the lifetime, for instance through corrosion or erosion, of e.g.coatings, sensors and/or (alignment) markers that come into contact withthe flow of immersion liquid (in particular substantially conductivecomponents of, e.g., coatings, sensors, and/or markers). In anembodiment, the conductivity of the liquid comprising the component isat least 0.1 μS/cm at 25° C., for instance at least 0.25 μS/cm, at least0.5 μS/cm, at least 0.75 μS/cm, at least 1 μS/cm, at least 1.3 μS/cm, atleast 1.5 μS/cm, at least 1.75 μS/cm, at least 2 μS/cm, at least 3μS/cm, at least 5 μS/cm, at least 10 μS/cm, at least 25 μS/cm, or atleast 50 μS/cm. While the above-mentioned and below-mentionedconductivities are determined at 25° C., the temperature at which theimmersion liquid is used may be different. The values referred to,however, remain the conductivities as determined at 25° C.

While increased conductivity may assist in reducing or eliminating theeffect of streaming potential, it may also increase the amount ofcomponent(s) that needs to be added to the immersion liquid, which maylead to staining or bubble concerns. In an embodiment, the conductivityof the liquid comprising the component is less than 50 mS/cm at 25° C.,e.g. less than 25 mS/cm, less than 10 mS/cm, less than 5 mS/cm, lessthan 1 mS/cm, less than 500 μS/cm, less than 250 μS/cm, less than 150μS/cm, less than 75 μS/cm, less than 50 μS/cm, less than 25 μS/cm, lessthan 15 μS/cm, less than 10 μS/cm, less than 7 μS/cm, less than 4 μS/cm,or less than 2 μS/cm. In an embodiment, the conductivity of the liquidis in the range of 0.1-100 μS/cm at 25° C., e.g. 0.25-25 μS/cm, 0.4-10μS/cm, or 0.6-6 μS/cm. In one embodiment, the conductivity of theliquid, e.g. an aqueous liquid, for instance ultra-pure water, isincreased by adding salts or acids to the liquid. In an embodiment, theliquid is enriched with acetic acid, formic acid, CO₂ (CO₂ may formin/with water the ions H⁺ and HCO₃ ⁻), or NH₃ (NH₃ may form in/withwater the ions NH₄ ⁺ and OH⁻).

Also, streaming potential may be reduced or avoided by decreasing thespeed and/or turbulence of the water flow. Furthermore, while notnecessarily avoiding streaming potential itself, providing a voltagedifference between the area effected by the streaming potential (e.g.the substrate table, for instance a sensor or a sensor plate on thesubstrate table) and another area may limit or negate the undesirableeffects caused by the streaming potential. In an embodiment, theinvention provides a lithography apparatus having a voltage generatorcapable of applying a voltage difference between a first part of alithography apparatus, e.g. the substrate table, and a second part ofthe lithography apparatus, e.g. the immersion hood of an immersionlithography apparatus. In an embodiment, the invention provides aprocess comprising applying a voltage difference between a first part ofa lithography apparatus, e.g. the substrate table, and a second part ofthe lithography apparatus, e.g. the immersion hood of an immersionlithography apparatus. In an embodiment, the voltage difference is atleast 0.1V, for instance at least 0.25V, at least 0.5V, at least 1V, atleast 2V, at least 3V, at least 4V, or at least 5V. In an embodiment,the voltage difference is less than 50V.

In an embodiment, the component added to the liquid is an acidiccomponent, e.g. acetic acid, formic acid, or carbon dioxide. Acidity ofthe immersion liquid may assist in maintaining the effectiveness ofresist that may come into contact with the immersion liquid, e.g. byhelping to slow down/decrease diffusion or dissolution of photo-acidgenerators that may be present in the resist, into the immersion liquid.In an embodiment, the liquid comprising the component has a pH below 7,e.g. below 6.5, below 6.0, below 5.5, below 5.0, below 4.5, or below4.0. In an embodiment, the pH is at least 2.0, such as at least 2.5, atleast 3.0, at least 3.5, at least 3.75, at least 4.0, at least 4.5, atleast 5.0, or at least 5.5. In an embodiment, the component added to theliquid is a base, e.g. ammonia (NH₃). Alkalinity of the immersion liquidmay assist in maintaining the effectiveness of resist that may come intocontact with the immersion liquid should the resist comprise alkalinecomponents (bases) rather than acid components that may leak into theimmersion liquid. In an embodiment, the liquid comprising the componenthas a pH above 7, e.g. above 7.5, above 8, above 8.5, above 9, above9.5, or above 10. In an embodiment, the pH is below 14.

The manner of adding the (one or more) component(s) to the liquid mayvary and may depend to an extent, e.g., on the type of component beingadded (e.g., whether it is available as a gas, a solid, or a liquid). Inan embodiment, the component is added via diffusion through a membrane.For instance, the liquid may flow on one side of a membrane and thecomponent on the other side of the membrane, whereby the membrane isimpermeable to the liquid but permeable to the component, thus allowingthe component to diffuse into liquid. In an embodiment, the componentthus added is a gas, e.g. CO₂. In an embodiment, the component is addedalong with one or more inert gases, e.g. N₂. Accordingly, in anembodiment, a liquid (e.g. an aqueous liquid, for instance ultra-purewater) flows on one side of the membrane and a CO₂/N₂ mixture flows onthe other side of the membrane, allowing CO₂ and N₂ to diffuse into theliquid. Commercial examples of suitable membrane equipment include,e.g., LIQUI-CEL membrane contactors from MEMBRANA. In an embodiment, thecomponent is added to the liquid by flowing (e.g., dripping) thecomponent into the liquid (or by flowing a comparatively concentratedcomponent/liquid solution into the liquid; e.g., when the component isammonia and the liquid is water, the ammonia may be added by flowing acomparatively concentrated aqueous ammonia solution into the water). Theadding of the (one or more) component(s) may be done remote from theapparatus (the immersion liquid may be “pre-prepared”), the adding maybe done in a separate unit that is linked to the apparatus (e.g., awater purification unit for the apparatus may be adapted for adding theone or more components), or the adding may be integrated into theapparatus.

PROCESS

The invention provides processes using the above-mentioned immersionliquids, for instance processes wherein a substrate is exposed toradiation and wherein the radiation passes through the immersion liquidbefore reaching the substrate.

In an embodiment, a process is provided comprising exposing a substrateto radiation, wherein the radiation has passed through an immersionliquid as described in the above section. In an embodiment, the processcomprises patterning a beam of radiation (e.g. with the aid of a reticleor an array of individually programmable elements), passing thepatterned beam through a projection system (e.g. an array of lenses),passing the patterned beam through the immersion liquid, and exposing aportion of the substrate with the patterned beam. In an embodiment, thesubstrate is a semiconductor substrate, e.g. a semiconductor wafer. Inan embodiment, the semiconductor substrate material is selected from thegroup consisting of Si, SiGe, SiGeC, SiC, Ge, GaAs, InP, and InAs. In anembodiment, the semiconductor substrate is a III/V semiconductorcompound. In an embodiment, the semiconductor substrate is a siliconsubstrate. In an embodiment, the substrate is a glass substrate. In anembodiment, the substrate is a ceramic substrate. In an embodiment, thesubstrate is an organic substrate, e.g. a plastic substrate. In anembodiment, the substrate is a photosensitive substrate, e.g. by havingcoated the substrate with a layer of resist.

In an embodiment, a device manufacturing process is provided comprising:

-   -   (i) patterning a beam of radiation;    -   (ii) passing the patterned beam of radiation through an aqueous        liquid, the aqueous liquid comprising ions formed by a component        having a vapor pressure greater than 0.1 kPa;    -   (iii) exposing a photosensitive substrate to the patterned beam        of radiation.

Also, in an embodiment, a process is provided comprising:

-   -   (i) patterning a beam of radiation;    -   (ii) passing the patterned beam of radiation through a liquid        comprising an acid or a base, the acid or base having a vapor        pressure exceeding the vapor pressure of the liquid;    -   (iii) exposing a photosensitive substrate to radiation, wherein        the radiation has passed through the aqueous liquid comprising        the component prior to reaching the photosensitive substrate.

In an embodiment, the process is a lithography process, such as animmersion lithography process. An example of an apparatus for carryingout an immersion lithography process is shown in FIG. 1. The apparatusdepicted in FIG. 1 comprises:

an illumination system (illuminator) IL configured to condition aradiation beam PB (e.g. UV radiation or DUV radiation);

a support structure (e.g. a mask table) MT constructed to support apatterning device MA and connected to a first positioner PM configuredto accurately position the patterning device in accordance with certainparameters. The support structure supports, i.e. bears the weight of,the patterning device. It holds the patterning device in a manner thatdepends on the orientation of the patterning device, the design of thelithographic apparatus, and other conditions, such as for examplewhether or not the patterning device is held in a vacuum environment.The support structure can use mechanical, vacuum, electrostatic or otherclamping techniques to hold the patterning device. The support structuremay be a frame or a table, for example, which may be fixed or movable asrequired. The support structure may ensure that the patterning device isat a desired position, for example with respect to the projectionsystem. The term “patterning device” used herein should be broadlyinterpreted as referring to any device that can be used to impart aradiation beam with a pattern in its cross-section such as to create apattern in a target portion of the substrate. It should be noted thatthe pattern imparted to the radiation beam may not exactly correspond tothe desired pattern in the target portion of the substrate, for exampleif the pattern includes phase-shifting features or so called assistfeatures. Generally, the pattern imparted to the radiation beam willcorrespond to a particular functional layer in a device being created inthe target portion, such as an integrated circuit. The patterning devicemay be transmissive or reflective. Examples of patterning devicesinclude masks and arrays of individually programmable elements (e.g.,programmable mirror arrays or programmable LCD panels). Masks are wellknown in lithography, and include mask types such as binary, alternatingphase-shift, and attenuated phase-shift, as well as various hybrid masktypes. An example of a programmable mirror array employs a matrixarrangement of small mirrors, which can be individually tilted so as toreflect an incoming radiation beam in different directions. The tiltedmirrors impart a pattern in a radiation beam which is reflected by themirror matrix.

a substrate table (e.g. a wafer table) WT constructed to hold asubstrate (e.g. a resist-coated wafer) W and connected to a secondpositioner PW configured to accurately position the substrate inaccordance with certain parameters. In an embodiment, the wafer tablecomprises one or more sensors (not shown), e.g. an image sensor (forinstance a transmission image sensor), a dose sensor, and/or anaberration sensor. In an embodiment, one or more of the sensors compriseone or more metals, e.g. chromium. In an embodiment, one or more of thesensors are coated, e.g. with titanium nitride.

a projection system (e.g., a refractive projection lens system) PLconfigured to project a pattern imparted to the radiation beam PB bypatterning device MA onto a target portion C (e.g. comprising one ormore dies) of the substrate W.

The illumination system may include various types of optical components,such as refractive, reflective, magnetic, electromagnetic, electrostaticor other types of optical components, or any combination thereof, fordirecting, shaping, or controlling radiation. The term “projectionsystem” used herein should be broadly interpreted as encompassing anytype of projection system, including refractive, reflective,catadioptric, magnetic, electromagnetic and electrostatic opticalsystems, or any combination thereof, as appropriate for the exposureradiation being used, or for other factors such as the use of theimmersion liquid or the use of a vacuum. In an embodiment, theprojection system includes an array of lenses. In an embodiment, theapparatus comprises an array of projection systems, e.g. to increasethroughput.

As here depicted, the apparatus is of a transmissive type (e.g.employing a transmissive mask). Alternatively, the apparatus may be of areflective type (e.g. employing a programmable mirror array of a type asreferred to above, or employing a reflective mask).

The lithographic apparatus may be of a type having two (dual stage) ormore substrate tables (and/or two or more mask tables). In such“multiple stage” machines the additional tables may be used in parallel,or preparatory steps may be carried out on one or more tables while oneor more other tables are being used for exposure.

Referring to FIG. 1, the illuminator IL receives a radiation beam from aradiation source SO. The source and the lithographic apparatus may beseparate entities, for example when the source is an excimer laser. Insuch cases, the source is not considered to form part of thelithographic apparatus and the radiation beam is passed from the sourceSO to the illuminator IL with the aid of a beam delivery system BDcomprising, for example, suitable directing mirrors and/or a beamexpander. In other cases the source may be an integral part of thelithographic apparatus, for example when the source is a mercury lamp.The source SO and the illuminator IL, together with the beam deliverysystem BD if required, may be referred to as a radiation system. In anembodiment, the radiation provided by radiation source SO has awavelength of at least 50 nm, e.g. at least 100 nm, at least 150 nm, atleast 175 nm, at least 200 nm, at least 225 nm, at least 275 nm, atleast 325 nm, at least 350 nm, or at least 360 nm. In an embodiment, theradiation provided by radiation source SO has a wavelength of at most450 nm, e.g. at most 425 nm, at most 375 nm, at most 360 nm, at most 325nm, at most 275 nm, at most 250 nm, at most 225 nm, at most 200 nm, orat most 175 nm. In an embodiment, the radiation has a wavelength of 365nm, 355 nm, 248 nm, or 193 nm.

The illuminator IL may comprise an adjuster AD for adjusting the angularintensity distribution of the radiation beam. Generally, at least theouter and/or inner radial extent (commonly referred to as σ-outer andσ-inner, respectively) of the intensity distribution in a pupil plane ofthe illuminator can be adjusted. In addition, the illuminator IL maycomprise various other components, such as an integrator IN and acondenser CO. The illuminator may be used to condition the radiationbeam, to have a desired uniformity and intensity distribution in itscross-section.

The radiation beam PB is incident on the patterning device MA, which isheld by the support structure MT, and is patterned by the patterningdevice. Having traversed the patterning device, the radiation beam PBpasses through the projection system PL, which focuses the beam onto atarget portion C of the substrate W. An immersion hood IH, which isdescribed further below, supplies immersion liquid to a space betweenthe final element of the projection system PL and the substrate W. In anembodiment, the substrate table WT and immersion hood IH are connectedto a voltage generator V (e.g., a battery) that is capable of providinga voltage difference between the substrate table WT and the immersionhood IH (e.g. between a sensor plate of substrate table WT and theimmersion hood H).

With the aid of the second positioner PW and position sensor IF (e.g. aninterferometric device, linear encoder or capacitive sensor), thesubstrate table WT can be moved accurately, e.g. so as to positiondifferent target portions C in the path of the radiation beam PB.Similarly, the first positioner PM and another position sensor (which isnot explicitly depicted in FIG. 1) can be used to accurately positionthe patterning device MA with respect to the path of the radiation beamPB, e.g. after mechanical retrieval from a mask library, or during ascan. In general, movement of the support structure MT may be realizedwith the aid of a long-stroke module (coarse positioning) and ashort-stroke module (fine positioning), which form part of the firstpositioner PM. Similarly, movement of the substrate table WT may berealized using a long-stroke module and a short-stroke module, whichform part of the second positioner PW. In the case of a stepper (asopposed to a scanner) the support structure MT may be connected to ashort-stroke actuator only, or may be fixed. Patterning device MA andsubstrate W may be aligned using alignment marks M1, M2 and substratealignment marks P1, P2. Although the substrate alignment marks asillustrated occupy dedicated target portions, they may be located inspaces between target portions (these are known as scribe-lane alignmentmarks).

Similarly, in situations in which more than one die is provided by thepatterning device MA, the alignment marks may be located between thedies.

The depicted apparatus could be used in at least one of the followingmodes:

1. In step mode, the support structure MT and the substrate table WT arekept essentially stationary, while an entire pattern imparted to theradiation beam is projected onto a target portion C at one time (i.e. asingle static exposure). The substrate table VVT is then shifted in theX and/or Y direction so that a different target portion C can beexposed. In step mode, the maximum size of the exposure field limits thesize of the target portion C imaged in a single static exposure.

2. In scan mode, the support structure MT and the substrate table VVTare scanned synchronously while a pattern imparted to the radiation beamis projected onto a target portion C (i.e. a single dynamic exposure).The velocity and direction of the substrate table WT relative to thesupport structure MT may be determined by the (de-)magnification andimage reversal characteristics of the projection system PL. In scanmode, the maximum size of the exposure field limits the width (in thenon-scanning direction) of the target portion in a single dynamicexposure, whereas the length of the scanning motion determines theheight (in the scanning direction) of the target portion.

3. In another mode, the support structure MT is kept essentiallystationary holding a programmable patterning device, and the substratetable WT is moved or scanned while a pattern imparted to the radiationbeam is projected onto a target portion C. In this mode, generally apulsed radiation source is employed and the programmable patterningdevice is updated as required after each movement of the substrate tableWT or in between successive radiation pulses during a scan. This mode ofoperation can be readily applied to maskless lithography that utilizesprogrammable patterning device, such as a programmable mirror array of atype as referred to above.

Combinations and/or variations on the above described modes of use orentirely different modes of use may also be employed.

FIG. 2 illustrates an embodiment of an immersion hood IH. Immersion Hood10 forms a contactless seal to the substrate around the image field ofthe projection system so that immersion liquid 11 is confined to fill aspace between the substrate surface and the final element of theprojection system. The reservoir is formed by a seal member 12positioned below and surrounding the final element of the projectionsystem PL. Immersion liquid 11 is brought into the space below theprojection system and within the seal member 12. The seal member 12extends a little above the final element of the projection system andthe liquid level rises above the final element so that a buffer ofliquid is provided. The seal member 12 has an inner periphery that atthe upper end, in an embodiment, closely conforms to the shape of theprojection system or the final element thereof and may, e.g., be round.At the bottom, the inner periphery closely conforms to the shape of theimage field, e.g., rectangular though this need not be the case.

The immersion liquid 11 is confined in the immersion hood 10 by a gasseal 16 between the bottom of the seal member 12 and the surface of thesubstrate W. The gas seal is formed by gas, e.g. air or synthetic airbut, in an embodiment, N₂ or an inert gas, provided under pressure viainlet 15 to the gap between seal member 12 and substrate and extractedvia first outlet 14. The overpressure on the gas inlet 15, vacuum levelon the first outlet 14 and geometry of the gap are arranged so thatthere is a high-velocity gas flow inwards that confines the liquid.

PRODUCTS

Some examples of devices that can be created with the present processand system include, e.g., micro electromechanical systems (“MEMS”), thinfilm heads, integrated passive components, image sensors, integratedcircuits (“ICs”)—including, e.g., power ICs, analog ICs, and discreteICs—, and liquid crystal displays.

In an embodiment, there is provided a device manufacturing processcomprising: (i) adding a component to a liquid, the component having avapor pressure greater than 0.1 kPa, e.g. greater than water; and (ii)exposing a photosensitive substrate to radiation, wherein the radiationhas passed through the aqueous liquid comprising the component prior toreaching the photosensitive substrate; wherein the adding of thecomponent increases the ion concentration in the liquid.

In an embodiment, the component has a vapor pressure greater than water.In an embodiment, the component lowers the pH of the liquid. In anembodiment, the component raises the pH of the liquid. In an embodiment,the component has a vapor pressure of at least 1 kPa. In an embodiment,the liquid comprises, relative to the total weight of the liquid, atleast 90 wt % of water. In an embodiment, the liquid comprises, relativeto the total weight of the liquid, at least 99.9 wt % of water. In anembodiment, the component is a gas at 20° C. and atmospheric pressure.In an embodiment, the liquid comprising the component has a pH in therange of 4.5-6.0. In an embodiment, the component is carbon dioxide orammonia. In an embodiment, the liquid comprising the component isessentially absent components having a vapor pressure lower than 2.0kPa. In an embodiment, the substrate is a semiconductor wafer coatedwith a layer of resist. In an embodiment, the radiation is UV radiationhaving a wavelength in the range of 175 nm-375 nm. In an embodiment, theprocess further comprises passing the radiation through an array oflenses prior to passing the radiation through the liquid comprising thecomponent. In an embodiment, the process further comprises patterningthe radiation prior to passing the radiation through the liquidcomprising the component. In an embodiment, the patterning is effectedwith a mask or an array of individually programmable elements. In anembodiment, the photosensitive substrate rests on a substrate tableduring the exposing, the substrate table comprising a sensor, the sensorcomprising titanium nitride and/or a metal. In an embodiment, theprocess comprises adding at least 2 components having a vapor pressureof at least 0.1 kPa to the liquid.

In an embodiment, there is provided a device manufacturing processcomprising: (i) adding an acid or base to a liquid, the acid or basehaving a vapor pressure of at least 0.1 kPa; and (ii) exposing aphotosensitive substrate to radiation, wherein the radiation has passedthrough the liquid comprising the component prior to reaching thephotosensitive substrate.

In an embodiment, the process comprises adding an acid to the liquid. Inan embodiment, the process comprises adding a base to the liquid.

In an embodiment, there is provided a device manufacturing processcomprising: (i) patterning a beam of radiation; (ii) passing thepatterned beam of radiation through a liquid, the liquid comprising ionsformed by a component having a vapor pressure greater than 0.1 kPa, theconductivity of the aqueous liquid being at least 0.25 μS/cm (asdetermined at 25° C.); and (iii) exposing a photosensitive substrate tothe patterned beam of radiation.

In an embodiment, there is provided a device manufactured with theprocess as described above. In an embodiment, the device is anintegrated circuit.

In an embodiment, there is provided an immersion lithography systemcomprising: (i) an immersion lithography exposure apparatus; and (ii) animmersion liquid having an electric conductivity in the range of 1.3-100μS/cm (as determined at 25° C.)

In an embodiment, the conductivity is at least 5 μS/cm. In anembodiment, the conductivity is at most 50 μS/cm. In an embodiment, theconductivity is in the range of 2-10 μS/cm. In an embodiment, theimmersion liquid is formed by adding a salt, a base, or an acid to anaqueous liquid. In an embodiment, the immersion liquid comprises carbondioxide. In an embodiment, the immersion liquid has a pH below 6.0. Inan embodiment, the immersion lithography exposure apparatus includes asubstrate table having a sensor comprising chromium and/or titaniumnitride. In an embodiment, the conductivity is caused at least in partby a component having a vapor pressure greater than 5 kPa.

In an embodiment, there is provided a lithography apparatus having avoltage generator functionally connected to a first part of alithography apparatus, the first part being a substrate table, andfunctionally connected to a second part of the lithography apparatus,the voltage generator being capable of establishing a voltage differencebetween the first part and the second part.

In an embodiment, the lithography apparatus is an immersion lithographyapparatus and the second part is an immersion hood.

Having described specific embodiments of the invention, it will beunderstood that many modifications thereof will readily appear or may besuggested to those skilled in the art, and it is intended therefore thatthis invention is limited only by the spirit and scope of the followingclaims.

What is claimed is:
 1. A lithographic apparatus comprising: a membrane impermeable to a liquid and permeable to a gas; a liquid inlet configured to supply a flow of the liquid to a first side of the membrane; a gas inlet configured to supply to a second side of the membrane a flow of the gas which diffuses through the membrane to dissolve in the liquid; and a liquid confinement structure configured to at least partly confine at least part of the liquid having the dissolved gas to a space between a final element of a projection system of the lithographic apparatus and a radiation-sensitive substrate so as to have the liquid having the dissolved gas at least contact the substrate and so that the substrate is arranged to receive a beam of radiation from the projection system via the liquid having the dissolved gas in the space.
 2. The apparatus of claim 1, wherein the liquid comprises water.
 3. The apparatus of claim 1, wherein the liquid is ultra-pure water.
 4. The apparatus of claim 1, wherein the gas comprises carbon dioxide.
 5. The apparatus of claim 1, wherein the gas, when combined with the liquid, acidifies the liquid.
 6. The apparatus of claim 1, wherein the gas is at least a mixture of carbon dioxide with one or more inert gases.
 7. The apparatus of claim 1, wherein the liquid having the dissolved gas has a pH below 6.0.
 8. The apparatus of claim 1, further comprising: the projection system configured to project a radiation beam onto the radiation-sensitive substrate; and a substrate table configured to support the substrate.
 9. The apparatus of claim 8, further comprising a voltage generator functionally connected to a first part of the lithographic apparatus, and to a second part of the lithographic apparatus, the voltage generator configured to establish a voltage difference between the first part and the second part.
 10. The apparatus of claim 9, wherein (i) the first part is the substrate table and the second part is the liquid confinement structure, and/or (ii) the first part is a sensor or sensor plate and the second part is the liquid confinement structure.
 11. A device manufacturing method comprising: providing a liquid on one side of a membrane; providing a gas on another side of the membrane, wherein the gas diffuses across the membrane to diffuse into the liquid; and projecting a radiation beam, in an immersion lithography apparatus, via at least part of the liquid comprising the diffused gas, onto a substrate in contact with the liquid comprising the diffused gas.
 12. The method of claim 11, wherein the gas acidifies the liquid.
 13. The method of claim 11, wherein the gas comprises carbon dioxide.
 14. The method of claim 11, further comprising establishing a voltage difference between a substrate table holding the substrate and a liquid confinement structure of the immersion lithography apparatus.
 15. The method of claim 11; wherein the liquid comprising the diffused gas has an electric conductivity in the range of 1.3-100 μS/cm (as determined at 25° C.) and a pH about equal to or below 6.5.
 16. A lithographic apparatus comprising: a source, or a connection thereto, the source having, in a use, a material configured to acidify a liquid; an inlet configured to supply liquid to a first region; a further inlet configured to supply the material to a second region adjacent the liquid such that at least part of the material diffuses into the liquid to at least acidify at least part of the liquid; and a liquid confinement structure configured to at least partly confine at least part of the acidified liquid to a space between a projection system of the lithographic apparatus and a radiation-sensitive substrate so that the acidified liquid at least contacts the substrate, the projection system configured to project a beam of radiation onto the radiation-sensitive substrate via the acidified liquid in the space.
 17. The apparatus of claim 16, wherein the material comprises a gas comprising carbon dioxide.
 18. The apparatus of claim 17, wherein the source has essentially only carbon dioxide gas as the gas or essentially only a combination of carbon dioxide gas and one or more inert gases as the gas.
 19. The apparatus of claim 16, configured to control the supply of the gas such that the acidified liquid has an electric conductivity in the range of 1.3-100 μS/cm (as determined at 25° C.) and a pH about equal to or below 6.5.
 20. The apparatus of claim 16, further comprising a membrane permeable to the gas and through which the gas can pass in order to diffuse into the at least part of the liquid. 